Conventionally, a bit selector is rotatably attached to the tip of the grip handle for choosing a driver bit stored in the grip handle. The selected driver bit selected by the selector becomes supported at the crevice of the handle tip, thereby making rotation of the bit difficult. The handle also forms the cap which houses a bit to be used and prevents unnecessary projection thereof. Thus, because the selector and the cap have been provided in the tip part of the grip handle, the structure has been complicated, costly, and further, the bits have been difficult to store.